So as far as I can see, Allegro 5 programs now properly compile with the
C++11 standard in use.

Do we really need to replace off_t with int64_t though? I mean better
safe than sorry, but are we really ever going to deal with file system
entries larger than 4GB? Where does the issue with using off_t on 64 bit
systems come in? If we needed file system offsets I would agree that
int64_t would be better, but I don't see any of that in use at the moment.